Process for the Preparation of Fluoroolefin Compounds

ABSTRACT

The subject of the invention is a process for the preparation of fluoroolefin compounds. It relates more particularly to a process for manufacturing a (hydro)fluoroolefin compound comprising (i) bringing at least one compound comprising from three to six carbon atoms, at least two fluorine atoms and at least one hydrogen atom, provided that at least one hydrogen atom and one fluorine atom are located on adjacent carbon atoms, into contact with potassium hydroxide in a stirred reactor, containing an aqueous reaction medium, equipped with at least one inlet for the reactants and with at least one outlet, in order to give the (hydro)fluoroolefin compound, which is separated from the reaction medium in gaseous form, and potassium fluoride, (ii) bringing the potassium fluoride formed in (i) into contact, in an aqueous medium, with calcium hydroxide in order to give potassium hydroxide and to precipitate calcium fluoride, (iii) separation of the calcium fluoride precipitated in step (ii) from the reaction medium and (iv) optionally, the reaction medium is recycled after optional adjustment of the potassium hydroxide concentration to step (i).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 13/144,239, filed Oct. 3, 2011, which is a National Phaseapplication of International Application No. PCT/FR2010/050043, filedJan. 12, 2010, which claims priority under 35 U.S.C. §119 to FrenchPatent Application No. FR0950157, filed Jan. 13, 2009.

FIELD OF THE INVENTION

The subject of the invention is a process for the preparation offluoroolefin compounds. The invention relates more particularly to aprocess for the preparation of hydrofluoropropenes.

TECHNOLOGICAL BACKGROUND

Hydrofluorocarbons (HFCs) and in particular hydrofluoroolefins (HFOs),such as 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), are compounds knownfor their properties of refrigerants and heat-exchange fluids,extinguishers, propellants, foaming agents, blowing agents, gaseousdielectrics, polymerization medium or monomer, support fluids, agentsfor abrasives, drying agents and fluids for energy production units.Unlike CFCs and HCFCs, which are potentially dangerous to the ozonelayer, HFOs do not comprise chlorine and thus do not present a problemfor the ozone layer.

1,2,3,3,3-Pentafluoropropene (HFO-1225ye) is a synthetic intermediate inthe manufacture of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf).

The majority of the processes for the manufacture of hydrofluoroolefinsinvolve a dehydrohalogenation reaction. Thus, the document WO 03/027051describes a process for the manufacture of fluoroolefins of formulaCF₃CY═CX_(n)H_(p), in which X and Y each represent a hydrogen atom or ahalogen atom chosen from fluorine, chlorine, bromine or iodine and n andp are integers and can independently take the value zero, 1 or 2,provided that (n+p)=2, which comprises bringing a compound of formulaCF₃C(R¹ _(a)R² _(b))C(R³ _(c)R⁴ _(d)), with R¹, R², R³ and R⁴independently representing a hydrogen atom or a halogen atom chosen fromfluorine, chlorine, bromine or iodine, provided that at least one of R¹,R², R³ and R⁴ is a halogen atom and that at least one hydrogen atom andone halogen atom are situated on adjacent carbon atoms, a and b beingable independently to take the value zero, 1 or 2, provided that(a+b)=2, and c and d being able independently to take the value zero, 1,2 or 3, provided that (c+d)=3, into contact with at least one alkalimetal hydroxide in the presence of a phase transfer catalyst.

This document teaches, in Example 2, that, in the absence of a phasetransfer catalyst, there is no reaction when1,1,1,3,3-pentafluoropropane (HFC-245fa) is brought into contact with a50% by weight aqueous potassium hydroxide (KOH) solution at ambienttemperature and under pressure for 24 hours.

In addition, this document teaches a reaction temperature of between−20° C. and 80° C.

The document WO 2008/075017 illustrates the dehydrofluorination reactionof 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to give1,2,3,3,3-pentafluoropropene (HFO-1225ye) at 150° C. in the presence ofa 50% by weight aqueous KOH solution. In the absence of a phase transfercatalyst, the conversion after 3 and a half hours is 57.8% and theselectivity for HFO-1225ye is 52.4% (Test 1). In the presence of a phasetransfer catalyst, this conversion is reached after only 2.5 hours andthe selectivity is virtually unchanged (Test 4). As indicated in Table 2of this document, it is necessary to use an organic solvent in order toincrease the selectivity for HFO-1225ye.

WO 2007/056194 describes the preparation of HFO-1234yf bydehydrofluorination of 1,1,1,2,3-pentafluoropropane (HFC-245eb) eitherwith an aqueous KOH solution or in the gas phase in the presence of acatalyst, in particular over a catalyst based on nickel, carbon or acombination of these.

The document Knunyants et al., Journal of the USSR Academy of Sciences,Chemistry Department, “Fluoroolefin Reactions”, Report 13, “CatalyticHydrogenation of Perfluoroolefins”, 1960, clearly describes variouschemical reactions on fluorinated compounds. This document describes thedehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (236ea) by passingthrough a suspension of KOH powder in dibutyl ether, to produce1,2,3,3,3-pentafluoro-1-propene (HFO-1225ye) with a yield of only 60%.This document also describes the dehydrofluorination of1,1,1,2,3-pentafluoropropane (HFC-245 eb) to give2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) by passing into a suspensionof KOH powder in dibutyl ether with a yield of only 70%.

Furthermore, FIG. 2 on page 51 of Part 2 of the nouveau traité de chimieminérale [New Treatise on Inorganic Chemistry] by P. Pascal, Ed. 1963,shows the appearance of the liquid/solid equilibria of the water andpotassium hydroxide system and the measurements are collated in theTable on page 52.

The dehydrofluorination reactions such as described above result,besides the desired hydrofluoroolefin compound, in the formation ofwater and potassium fluoride. Furthermore, the implementation of such areaction in continuous mode is not easy on an industrial scale since atleast three phases (gas, liquid and solid) are involved.

The present invention provides a process for the continuous andsemi-continuous manufacture of a (hydro)fluoroolefin compound that makesit possible to overcome the aforementioned drawbacks.

The subject of the present invention is therefore a process for thecontinuous or semi-continuous manufacture of a (hydro)fluoroolefincompound comprising (i) bringing at least one compound comprising fromthree to six carbon atoms, at least two fluorine atoms and at least onehydrogen atom, provided that at least one hydrogen atom and one fluorineatom are located on adjacent carbon atoms, into contact with potassiumhydroxide in a stirred reactor, containing an aqueous reaction medium,equipped with at least one inlet for the reactants and with at least oneoutlet, in order to give the (hydro)fluoroolefin compound, which isseparated from the reaction medium in gaseous form, and potassiumfluoride, (ii) bringing the potassium fluoride formed in (i) intocontact, in an aqueous medium, with calcium hydroxide in order to givepotassium hydroxide and to precipitate calcium fluoride, (iii)separation of the calcium fluoride precipitated in step (ii) from thereaction medium and (iv) optionally, the reaction medium is recycledafter optional adjustment of the potassium hydroxide concentration tostep (i).

The present invention thus makes it possible to obtain an advantageousprocess since, on the one hand, potassium hydroxide is more reactivethan calcium hydroxide in the dehydrofluorination reaction and, on theother hand, calcium fluoride is a reusable by-product. The processaccording to the present invention preferably provides a(hydro)fluoroolefin compound comprising three carbon atoms,advantageously a (hydro)fluoroolefin compound represented by the formula(I):

CF₃CY═CX_(n)H_(p)  (I)

in which Y represents a hydrogen atom or a halogen atom chosen fromfluorine, chlorine, bromine or iodine and X represents a halogen atomchosen from fluorine, chlorine, bromine or iodine; n and p are integersand may independently take the value zero, 1 or 2 provided that (n+p)=2,by bringing a compound of formula CF₃CYRCR′X_(n)H_(p), in which X, Y, nand p have the same meaning as in formula (I) and R represents afluorine atom when R′ represents a hydrogen atom or R represents ahydrogen atom when R′ represents a fluorine atom into contact withpotassium hydroxide.

The present invention is very particularly suitable for the manufactureof a compound of formula (Ia):

CF₃—CF═CHZ  (Ia)

in which Z represents a hydrogen or fluorine atom, from a compound offormula CF₃CFRCHR′Z, in which Z has the same meaning as in formula (Ia)and R represents a fluorine atom when R′ represents a hydrogen atom or Rrepresents a hydrogen atom when R′ represents a fluorine atom.

Thus, 2,3,3,3-tetrafluoropropene may be obtained by dehydrofluorinationof 1,2,3,3,3-pentafluoropropane with KOH and/or1,2,3,3,3-pentafluoropropene by dehydrofluorination of1,1,1,2,3,3-hexafluoropropane with KOH. The 1,2,3,3,3-pentafluoropropenemay be in the cis and/or trans isomer form.

The present invention may also be used for the manufacture of1,3,3,3-tetrafluoropropene by dehydrofluorination of1,1,3,3,3-pentafluoropropane with KOH.

In the remainder of the text, the limits of the concentration andtemperature ranges given are included in said ranges.

In step (i) of the process according to the present invention, thepotassium hydroxide may represent between 10 and 90% by weight relativeto the weight of the water and KOH mixture present in the aqueousreaction medium, preferably between 20 and 86% and advantageouslybetween 55 and 75% by weight. Depending on the content, the potassiumhydroxide may be in the form of an aqueous solution or in the moltenstate. This high KOH content leads to an increase in the conversion rateof the hydrofluoroalkane to hydrofluoroalkene. Moreover, due to thisconcentrated KOH medium, the HF formed in (i) reacts immediately withKOH to form KF that is less corrosive than HF, which makes it possibleto use, downstream of the dehydrofluorination reactor, carbon steelreactors that are of low cost compared to reactors made of an inertmaterial (UB6 or Inconel) for the dehydrofluorination reactor. Moreover,the “trapping” of HF in the form of KF facilitates the separation of thevarious products from one another (HF having a tendency to formazeotropes with hydrofluoroalkanes and hydrofluoroalkenes), thus, asimple distillation is sufficient to separate the products from oneanother.

The step (i) is generally carried out at a temperature such that thewater formed during the dehydrofluorination reaction is removed, partlyor completely, from the reaction medium via entrainment of the gasstream comprising the (hydro)fluoroolefin compound from the stirredreactor. This temperature is preferably between 80 and 180° C.,advantageously between 125 and 180° C., and very particularly between145 and 165° C. The evaporation of the water during step (i) is in thedirection of increasing the conversion rate of the hydrofluoroalkane tohydrofluoroalkene.

The dehydrofluorination reaction of step (i) may be carried out atatmospheric pressure, but it is preferred to work at a pressure aboveatmospheric pressure. Advantageously, this pressure is between 1.1 and2.5 bar.

The reaction of step (ii) may be carried out in a stirred reactor orfluidized bed reactor by reacting calcium hydroxide, preferably in asuspension in water, with the potassium fluoride from step (i). Thereaction temperature may vary to a large extent but for economicreasons, it is preferably between 50 and 150° C., for example from 75°C. to 120° C. and advantageously between 90 and 120° C.

When a suspension of calcium hydroxide is used in step (ii), the calciumhydroxide represents between 2 and 40% by weight relative to the weightof the suspension.

Advantageously, step (ii) is carried out in the reaction medium fromstep (i) comprising water, potassium hydroxide and potassium chloride.The potassium fluoride originating from step (i) and supplying step (ii)may be dissolved or in suspension.

The potassium hydroxide represents, in the reaction medium of step (ii),preferably between 2 and 50% by weight relative to the weight of thewater and potassium hydroxide mixture of the medium.

When the steps (i) and (ii) are carried out in separate reactors, it ispossible to provide a dilution step of the reaction medium between step(i) and step (ii).

The calcium fluoride precipitated in step (ii) is separated from thereaction medium, for example by filtration and/or settling. Prior to thefiltration, it is possible to provide a settling step. The calciumfluoride thus separated is then washed with water.

During the settling step, it is possible to make provision for therecycling of a portion of the suspension that is concentrated in calciumfluoride to step (ii). Advantageously, the content of calcium fluoridesolids present in the reaction medium of step (ii) is between 5 and 40%by weight.

After separation of the calcium fluoride, the reaction medium with orwithout the calcium fluoride washing waters may be recycled to step (i)after optional adjustment of the potassium hydroxide content.

According to one embodiment of the invention, steps (i) and (ii) may becarried out in the same reactor.

It may be advantageous to use an inert gas, preferably nitrogen orhydrogen in the dehydrofluorination step.

The process according to the present invention has the advantage ofresulting in high yields even in the absence of a phase transfercatalyst and/or an organic solvent.

The present invention also comprises the combinations of the preferredforms regardless of the embodiment.

EXPERIMENTAL SECTION Example 1

FIG. 1 gives the diagram for one embodiment of the present invention. Astirred reactor (1), made of nickel, equipped with a device for heatingand measuring the temperature of the reaction medium, containing amixture of water and of KOH, is continuously fed with a solution ofmolten KOH (2) in which the KOH is present at 60% by weight in thewater, and with 1,1,1,2,3,3-hexafluoropropane (3). The temperature iskept at 160° C. and the pressure in the reactor is 1.2 bar absolute. Thegaseous products exit the reactor via an orifice (4) located in thecover of the reactor and the water contained in the gas stream isremoved by condensation (13). The outlet (5) of the reactor (1) isconnected to the inlet of the stirred reactor (6) and therefore providesthe reactor (6) with the supply of potassium hydroxide, which may be insuspension in the aqueous medium. A 10% by weight suspension of calciumhydroxide in water is introduced into the reactor (6) via the line (7).The reactor (6) is kept at a temperature between 100 and 120° C.

The outlet of the reactor (6) is connected to a filter (8) in order toseparate the calcium fluoride from the reaction medium, then wash itwith water introduced via the line (9); the aqueous medium separatedfrom the calcium fluoride and also the calcium fluoride washing watersare then recycled to the reactor (1) after adjustment of the KOHconcentration; the calcium fluoride is recovered via the line (12).

The mixture of molten KOH supplying the reactor (1) is prepared byheating (11) an aqueous solution of 50% by weight of KOH introduced bythe line (14) for the purposes of evaporation (removal of water (15)).

Example 2

The procedure of example 1 is followed except that the reactor (1) iscontinuously supplied with 1,2,3,3,3-pentafluoropropane instead of1,1,1,2,3,3-hexafluoropropane.

By using a KOH content higher than that from the prior art, improvedconversion rates of the hydrofluoroalkane to hydrofluoroalkene(therefore a better productivity), a reusable produce, CaF₂, and lowermanufacturing costs of the hydrofluoroalkene are obtained.

1-11. (canceled)
 12. A process for the manufacture of a fluoroolefincomprising: (a) dehydrofluorinating a fluoroalkane in the presence ofKOH to produce a fluoroalkene; (b) withdrawing a reaction streamcomprising spent KOH; and (c) recovering spent KOH.
 13. The process ofclaim 12 wherein the fluoroalkane is comprised of a compound of formulaCF₃CYRCR′X_(n)H_(p), in which Y represents a hydrogen atom or a halogenatom chosen from fluorine, chlorine, bromine or iodine and X representsa halogen atom chosen from fluorine, chlorine, bromine or iodine; n andp are integers and may independently take the value zero, 1 or 2provided that (n+p)=2, and R represents a fluorine atom when R′represents a hydrogen atom or R represents a hydrogen atom when R′represents a fluorine atom.
 14. The process of claim 13 wherein thefluoroalkane is 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) or1,1,1,2,3-pentafluoropropane (HFC-245eb).
 15. The process of claim 12wherein the fluoroalkene is comprised of a compound of formulaCF₃CY═CX_(n)H_(p) in which Y represents a hydrogen atom or a halogenatom chosen from fluorine, chlorine, bromine or iodine and X representsa halogen atom chosen from fluorine, chlorine, bromine or iodine; n andp are integers and may independently take the value zero, 1 or 2provided that (n+p)=2.
 16. The process of claim 15 wherein thefluoroalkene is 2,3,3,3-tetrafluoropropene (HFO-1234yf) or1,2,3,3,3-pentafluoropropene (HFO-1225ye).
 17. The process of claim 12wherein the dehydrofluorination occurs using a continuously stirred tankreactor.
 18. The process of claim 12 wherein the spent KOH is withdrawnfrom the reactor continuously or intermittently.
 19. The process ofclaim 12 wherein the spent KOH is purified using at least one separationmethod.
 20. The process of claim 19 wherein the separation method isphase separation.
 21. The process of claim 12 further comprising,optionally, concentrating the purified KOH and recycling it back to thedehydrofluorination reaction.
 22. The process of claim 12 wherein thereaction stream further comprises KF.
 23. The process of claim 22further comprising converting KF to KOH in the presence of Ca(OH)₂. 24.The process of claim 23 further comprising, optionally, concentratingthe converted KOH and recycling it back to the dehydrofluorinationreaction.
 25. A process for the manufacture of a fluoroolefincomprising: (a) dehydrohalogenating 1,1,1,2,3,3-hexafluoropropane(HFC-236ea) or 1,1,1,2,3-pentafluoropropane (HFC-245eb) in the presenceof KOH to produce 2,3,3,3-tetrafluoropropene (HFO-1234yf) or1,2,3,3,3-pentafluoropropene (HFO-1225ye); (b) withdrawing a reactionstream comprising spent KOH; and (c) recovering spent KOH.
 26. Theprocess of claim 25 wherein the dehydrohalogenation occurs using acontinuously stirred tank reactor.
 27. The process of claim 25 whereinthe spent KOH is withdrawn from the reactor continuously orintermittently.
 28. The process of claim 25 wherein the spent KOH ispurified using at least one separation method.
 29. The process of claim28, wherein the separation method is phase separation.
 30. The processof claim 25 further comprising, optionally, concentrating the purifiedKOH and recycling it back to the dehydrohalogenation reaction.
 31. Theprocess of claim 25 wherein the reaction stream further comprises KF.32. The process of claim 31 further comprising purifying KF from thereaction stream.
 33. The process of claim 25 further comprisingconverting KF to KOH in the presence of Ca(OH)₂, optionally,concentrating the KOH and recycling it back to the dehydrohalogenationreaction.
 34. A process for the manufacture of a fluoroolefincomprising: (a) dehydrohalogenating a haloalkane in the presence of KOHto produce a haloalkene; (b) withdrawing a reaction stream comprisingspent KOH; and (c) recovering spent KOH.